1. Field of the Invention
The present invention relates to an optical network provided with a plurality of nodes, and in particular to an optical switching system provided in an optical network to support communication between the nodes.
2. Description of the Related Art
Optical switching systems have been developed to exchange data traffic, such as IP packets and Ethernet frames, in order to overcome the limitations of conventional electric switching systems in speed and capacity.
Due to the explosive increase of Internet users, it is expected that data traffic will reach several Tb/s to tens of Tb/s in the future. In order to accommodate this, transmission networks are constructed based on a Dense-Wavelength-Division-Multiplexing (DWDM) mode. However, switching networks are still constructed based on electric switching systems, which are not easy to match w ith the D WDM optical transmission network. The switching capacity of electrical switching systems is limited to hundreds Gb/s or less due to the limitations in processing speed or the like of electric components. In addition, electric switching systems electrically convert and process not only dropped data, but also path-through data traffic. Therefore, the hardware becomes larger and more complex. In order to solve this problem, an OPDM (Optical Add/Drop Multiplexer) has been used, but is limted in that it cannot effectively use a bandwidth of an optical signal in an environment where data traffic is bursty.
Accordingly, in order to overcome the limitations in speed and capacity of conventional electric switching systems and to maximize the utilization of a bandwidth of an optical signal, optical switching systems have been researched, which exchange optical signals in terms of optical packet, burst or frame in an all-optical domain without electrically converting optical signals. One example of previously proposed optical switching systems is a broadcasting and selection mode switching system, which solves the problem of collisions between optical frames by performing a switching function using a beam splitter and an optical gate switch, then delaying the optical frames using a plurality of fiber optic delay lines.
A wavelength routing m ode system has been also proposed, which performs switching functions by converting a wavelength of an input optical frame at high speed according to an AWG (Arrayed Waveguide Grating) routing table using a high-speed variable wavelength converter and an AWG. This solves the problem of collisions by additionally using a high-speed wavelength converter, an optical delay line, and a wavelength division multiplexer/demultiplexer. Most of the proposed optical switching systems employ a high-speed variable wavelength converter in order to implement a switching function and an anti-collision function of optical packets, bursts or the like.
The wavelength converting speed of the above-mentioned systems are merely hundreds of μs to thousands of μs. Thus, these systems are not suitable for an optical switching system in which a switching speed in the range of several ns to tens of ns is required. A variable wavelength converter with a wavelength converting speed of several ns has been reported. However, there is a fundamental limitation in applying such a variable wavelength converter to an optical switching system because its wavelength has a variable width, which is limited and a time of tens of μs or more is needed for stabilization due to practical variations of the wavelength. There is also a problem in that because conventional optical systems require a number of variable wavelength converters, the hardware of those systems becomes very complex. When capacity expansion of an optical switching network is required, it is necessary that some wavelengths are added or the number of input and output links is increased. However, the previously proposed systems also reveal the limitations in expandability based on wavelength addition, increase of input and output links. Thus, these systems have a disadvantage in accommodating increasing capacity which is required by a network. In addition, in order to avoid collisions of optical data, a large number of fiber optic delay lines are needed, thereby further increasing complication and revealing a disadvantage in expansion of optical buffers when the capacity of optical buffers is required to be expanded. Furthermore, because most of the conventional systems employ a centralized system, there is a problem in that the control of optical switching systems is very complicated.